The use of one or more countershafts in heavy duty motor vehicle change gear transmissions to increase gear ratio availability is well known in the art and of which examples may be seen in U.S. Pat. Nos. 4,027,756 and 4,104,928, the disclosures of which are included herein by reference. Such countershafts carry gears that are driven and selectively drive the mainshaft gears. Such countershafts are rotationally supported on the transmission housing by bearing assemblies (commonly tapered roller bearing assemblies) with the inner race of the bearing being commonly press-fit onto the countershaft adjacent its opposite ends with the outer race being disposed and axially movable along a bore in the transmission housing.
Since it is essential to keep axial movement of the shaft to a minimum to prevent bearing and/or gear tooth wear and breakage, varying thickness shim discs having commonly been employed in the past to fill the gap in the housing bore between the outer race and an external cover plate covering the bore opening to control end play of the bearing assembly and of the shaft itself.
The use of such shim discs requires costly inventory of discs having varying thicknesses and even then one may not be able to effect the closeness of fit desired in addition to the fact that the shim discs cannot be adjusted for wear without the costly and time consuming task of having to remove the cover plate.
The present invention replaces such shim discs with a rotary shim member that can be rotationally advanced against the bearing assembly to minimize end play to the extent desired and then be releasably locked at that rotational position until readjustment is required at which time the rotary shim is released and rotationally advanced to a new rotational position and then again releasably locked at the new position.
The use of the threaded members to control end play of bearing assemblies is known and can be found for example in U.S. Pat. No. 4,229,017, the disclosure of which is included herein by reference and in which a threaded bolt optionally having a lock nut is used to prevent axial movement of a bearing assembly on a vehicle suspension king pin. Another example can be found in U.S. Pat. No. 4,033,644, the disclosure of which is included herein by reference, where a threaded device is used to compress Belville washers against a bearing assembly on a motor vehicle axle. Such devices however fail to include the rotational position locking member as an integral part of a rotary shim member and no one prior to the present invention recognized the great advantage in providing a threaded opening through the countershaft cover plate so as to enable the use of a threaded rotary shim member to minimize end play of the shaft bearing assembly to the extent desired without having to remove the cover plate.